Fuel injection and control system

ABSTRACT

A mass flow timed fuel injection system is provided wherein fuel flow is maintained at all times in a predetermined relation to air mass flow actually entering the engine at any instant, and the fuel injection valve open time is maintained in inverse proportion to speed or, is open for a constant crank angle.

I Unlted States Patent 1191 1111 3,817,231 ONeill 1 June 18, 1974 [54] FUEL INJECTION AND CONTROL SYSTEM 2,924,206 2/1960 Groves 123/119 R 2,957,464 10/1960 Dolza 123/139 AW [75] lnvemor- Cmna G-oNeuLafayeflecahf- 2,957,464 10/1960 DOlZfl .123/119 3 Assignee: physics International Company, San 3,036,564 5/1962 Gulot 123/32 EA Leandro Calif 3,181,520 5/1965 Mock 1 1 123/139 AL 3,319,613 5/1967 Begley 61211 123/32 EA [22] Filed: June 21, 1971 3,430,616 3/1969 GlOCklEl'Cl 211.. 123/32 EA ux 3,456,628 7/1969 Bassot et a1. 123/32 EA 1 1 pp o.: 155,220 3,470,858 10/1969 Mycroft 123/119 R 3,596,640 8/1971 Bloomfield 123/32 EA f' Appl'cam Data 3,683,750 9/1972 0116111 123/32 EA [63] Conunuauon of Ser. No. 858,717, Sept. 17, 1969,

abandoned.

Przmary Exammer-Laurence M. Goodndge 152 11.5. C1... 123/119 R, 123/32 EA, 123/139 AW Amid"! Emmmekcoft 51 1111.01. F02m 51/00 Attorney Agent Frelllch & [58] Field of Search 123/32 EA, 139, 140 Wasserman [5 6] References Cited 7 ABSTRACT UNITED STATES PATENTS [5 1 I 1 2 447,267 8/1948 Mock 123/119 R A g flow i 'J sysiem provided 2447,26? 8/1948 M I I 123 19 wherem fuel flow 13 mamtamed at all t1mes 1n a prede- 2:62|640 12/]952 Reggio I 123/90 13 termined relation to air mass flow actually entering 2,670,724 3/1954 Reggio .1 123/140 CC the engine at any instant, and the fuel injection valve 2,8569 I0 10/1958 Goodridge... 123/32 AE open time is maintained in inverse proportion to speed 2,899,948 8/1959 Groves 123 1403 or, is Open for a constant crank angle. 2,918,911 12/1959 Guiot 123/32 EA 19 Claims, 12 Drawing Figures OPEN DURATlON CONTROL TO 72L meme \NTAKE MANHIOLD MOTOR AL ERNATOR PATENTEDJun 18 m4 33171231 sum 5 or 8 //v VEN roe COPMAC G. O Ova/.1.

FUEL INJECTION AND CONTROL SYSTEM This application is a continuation of Serial No. 858,717, Sept. 17, 1969, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to fuel injection systems for internal combustion engines and more particularly to improvements therein. The fundamental principle of providing a fuel flow that is maintained at all times proportional to air mass flow is well known. The principle in volved uses an air meter (usually a venturi) and a fuel meter (usually a fuel jet) to obtain pressure drops proportional to the square of the air mass flow rate. These pressure drops are applied to devices known as movable wall devices in order to achieve an equilibrium position of a fuel spill valve in a manner to maintain the resulting fuel and .air forces in balance. The fuel-air ratio produced depends upon the choice of venturi throat area, fuel orifice area, diaphragm effective area, and spill valve effective area.

With such a system, accurate metering can be achieved at full throttle conditions but closure of the throttle immediately introduces metering errors. The fundamental force balance requires that the air signal be the pressure difference between atmospheric and venturi throat pressures and similarly that the fuel signal be the pressure drop across the fuel metering orifice. In presently known systemsfuel line pressure is used and as a result errors occur due to the pressure drop in the induction passages of the engine resulting from closure of the throttle to restrict engine power output, for example at idling and light cruising loads.

Presently known systems attempt correction of these errors by air bleeding the nozzle valves and thus attempt to bring the downstream side of the fuel orifice to (or nearly to) atmospheric pressure. However, the

quantity of air required effectively to bleed down depression on, for example, eight nozzles is such that idling speed is excessive. Also, those nozzles remain open at all times including during engine stopped condition. Consequently, the fuel lines discharge during the period following engine shut down giving restart difficulties. Another problem arises when starting, hot or cold, with air bled nozzles, due to the fact that the fuel lines are empty and there is a time lag in refilling them.

Known systems require that total fuel injection time, i.e., the sum of all intervals for each cylinder should be equal to total air flow time, and thus, they employ continuous flow injection. However, better control of fuel distribution, cylinder to cylinder, can be obtained if fuel delivery is discontinued during the engine inlet valve-closed time, since manifold wetting and kickback" of wet fuel are avoided. Breakdown of injection duration into discrete intervals poses problems of control, since, if a constant injection time per injection were used, an injection pressure regulated by the air mass flow signal would result in total fuel flow that would include the engine speed factor twice. For example, the total air consumption at 1,000 rpm of the engine when it is fully loaded is approximately equal to the total air consumption at 2,000 rpm at one-half load. Both conditions would consequently receive the same total air flow and the same resultant fuel pressure would be fed to the injection valves. If the injection valve was open for a constant time duration on each cycle, the 2,000 rpm half load condition would receive twice the total fuel flow of 1,000 rpm full load condition. 1

OBJECTS AND SUMMARY OF THE INVENTION An object of this invention is to provide a fuel injection system that employs a signal derived from air mass flow for determining fuel injection pressure and avoids high idling speed, metering errors, starting difficulties or constant injection time difficulties.

Yet another object of this invention is the provision of a mass flow timed fuel injection system which avoids problems at low engine output of inadequate fuel atomization and suppresses the formation of vapor which can prove troublesome.

Still another object of the present invention is the provision of a fuel injection system which injects exactly the amount of fuel for induction into each cylinder which that cylinder can burn.

These and other objects of the invention may be achieved in a common rail fuel delivery system for an internal combustion engine wherein the pressure at which fuel is applied to fuel injection valves is in proportion to the mass air flow, information for which is derived using a venturi and a spill valve and the duration of the fuel injection valve open time is varied inversely with engine speed. To avoid the formation of vapor at low engine output together with inadequate atomization, fuel pressure is prevented from falling below a predetermined minimum value which is preselected. At all operating power levels below this minimum value fuel pressure, it is apparent that mixture strength would be too rich. To maintain correct mixture strength under these conditions, a correction in fuel delivery valve-open duration is introduced that shortens the duration of injection in the relationship:

Where Ta is actual injection valve open duration, Ts is Injection valve open duration derived from fixed crank angle, Pv is Fuel injection pressure derived from mass air flow signal, and Pa is Actual fuel injection pressure. For these purposes the actual fuel pressure used is taken as the pressure differential between the fuel supply line and intake manifold pressure.

In addition, in order to avoid the problems produced by using constant time per injection, this invention holds valves open per cycle in inverse proportion with speed (or, the injection valve is open for a constant crank angle at all times when fuel injection pressure exceeds some predetermined level, such as 20 p.s.i.)

The novel features of the invention are set forth with particularity in the appended claims. The invention will best be understood from the following description when read in conjunction with the accompanying drawmgs.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic arrangement of an embodiment of the invention. a

FIG. 2 is a schematic circuit arrangement of the pulse duration control circuit employed in an embodiment of the invention.

FIG. 3 is a cross sectional view of a valve duration control system illustrative of another embodiment of the invention.

FIG. 4 is a view along the lines 4-4 of FIG. 3.

FIG. 5 is a partial sectional view of FIG. 3 showing a rack drive system.

FIG. 6 is an end view of FIG. 3.

FIG. 7 is a view along the lines 7-7 of FIG. 6.

FIGS. 8A and 8B are cross sectional views of the sleeve 180 taken along the lines 8-8 of FIG. 3 and 9-9 of FIG. 3.

FIG. 9 is a view in elevation of the sleeve 180.

FIG. 10 is a circuit diagram of an electrical logic arrangement for enerating a control signal representative of Pv/Pa, and

FIG. 11 is a cross section illustrating a fuel injection valve which may be employed with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic representation of a fuel injection and control system for an internal combustion engine in accordance with this invention.

A high pressure pump 10 is driven in approximately constant relationship to engine speed, either by direct coupling, or preferably, by an induction motor 12 which is powered directly from the AC output of the vehicle alternator 14. The pump 10, which may be a positive displacement pump, pumps fuel from a conventional float bowl 17. A float 16 enables fuel to be transferred into the float bowl 17 from the fuel tank, when the level of the fuel in the float bowl drops below a predetermined value.

The fuel is pumped to a plurality of injection valves 18A, 18N, one to each cylinder, which are fed from a common passage. The fuel is then circulated to a spill valve unit 20, and from the spill valve unit back to the float bowl 17 then to the injection valves. Each of the injection valves may be of an electro mechanical type that open and close very rapidly in response to an electrical signal, which is provided by open duration control system 22. The injection valve may also be of a hydraulically actuated type which responds to hydraulic pressures from the opening duration control 22. Each valve contains a calibrated orifice through which the fuel must pass before it can be discharged.

The spill valve unit 20 includes a cylindrical chamber 23 having a diaphragm 24 mounted therein. The diaphragm is attached to a poppet valve stem 26 which is supported in a guide bore 28. The lower part of the guide bore 28A is enlarged and the larger bore terminates in a narrow seating upon which the poppet valve 30 can seat. The poppet valve is free to slide on its stem but is urged toward the closed or seated position by a spring 32 mounted on the stem between the poppet and a snap ring or collar 34. To prevent the spring from drawing the stem downward and thus distorting the diaphragm, a collar 26A is formed at the upper end of the valve stem that abuts the spill valve housing when the diaphragm is in the lowest permitted position.

The air silencer and cleaner 36 is supported on one end of the air intake 38 which leads to a common plenum chamber or manifold (not shown) which distributes air to the intake ports of the engine. A venturi structure 40 is located in this intake. A throttle valve 42 is located between the venturi and the engine. Tappings in the throat of the venturi, 44, are connected via a tube 46, to the diaphragm chamber 23 of the spill valve unit 20, to apply vacuum to the upper side of the diaphragm 24, depending upon the flow of air through the venturi. The greater the flow of air, the greater the pull on the poppet valve, the less fuel can get by it and therefore the higher the back pressure of the fuel on the injection valves. The lower the flow of air through the venturi, the lower the pull on the diaphragm and the poppet valve, the more fuel can get by the poppet valve into the float chamber, and therefore the lower the pressure of the fuel on the injection valves.

A progression system and idling port 50, with a volume control tapered screw 52, and an air bleed from atmosphere 63, which are conventionally used in carburetors, are provided in the throttle body and the channel linking, idling and progression holes is connected to a third or idling pressure sensor 54, which will be described later herein. An air bleed line 56 is connected to the line 46 which is connected to the spill valve chamber. This air bleed line 56 connects to atmosphere through a rotating (or poppet) valve 58, which in turn is operated by the throttle movement so that during the 15 of travel preceding the full open position, the air bleed is completely shut off.

A first pressure sensor 60, comprises an upper chamber 60U which is separated from the lower chamber 60L by a diaphragm 60D. The diaphragm carries a magnetic core 62. A winding 66 senses the position of the core 62.

The upper chamber of the first pressure sensor 60 is connected to the upper side of the spill valve diaphragm chamber. The lower chamber of the first pressure sensor is connected via a pipe 68 to the lower side of the spill valve diaphragm chamber. The lower side of the spill valve diaphragm chamber also communicates via the pipe 70 with the float bowl. The first pressure sensor thus provides an electrical output representative of the difference in pressure across the diaphragm which is proportional to the intake air (mass flow) or to the fuel pressure that is being signalled to the injection valves. A tube 411 also extends from the air intake 38 to the tube 68 and then to the tube 70. An impact tube 43 is placed at the junction between tube 41 and air intake 38 to sense stagnation pressure in the intake passage.

A second pressure sensor 72 has a similar construction to the first pressure sensor. Its lower chamber 72L is connected via a tube 73 to the intake manifold downstream of the throttle valve 42. The upper chamber 72U is connected via a pipe 74 to the fuel passage in the spill valve unit 20 which is upstream of the poppet valve 30. An inductive pickup 76 on the second pressure sensor 72 senses the position of the diaphragm therein.

The electrical signal output of the second pressure sensor represents the actual fuel pressure difference applied across the calibration in the injection valves which is to be described later.

The idling pressure sensor 54 may be called the third 1 pressure sensor and is connected so that the idling and venturi 40 falls into a laminar flow regime and indicates flow erroneously.

The third pressure sensor output is used to indicate when the fuel pressure would fall below a predetermined value, for example below 20 lbs. per sq. in.. If the determination of fuel pressure remained solely under the control of mass air flow in the venturi, at low engine output there would be a low fuel pressure and vapor would be formed and there would be inadeauate atomization. The spring 32 establishes a minimum fuel pressure which avoids the effects of low fuel pressure. However, at engine operating levels below this minimum value fuel pressure, the mixture strength could become too rich. A correction is made by the open duration control 22, in the time duration the fuel delivery value is kept open, that shortens fuel injection time and thereby compensates and maintains the correct fuel mixture strength.

When the engine is first started, the choke valve 39 placed just before the venturi is turned to block the passage of air. This causes an increase in the differential air pressure across the diaphragm 24. The result is an upward pull on the diaphragm which pulls up on the spill valve. This results in increased pressure and fuel fiow to the fuel injection valves, a desirable condition during cold starting.

As previously indicated, the injection valves may be mechanically, hydraulically, or electrically driven, but the drive is such that the valves remain open for a fixed crank angle duration. in the event that electrically driven fuel injection valves are desired, then a duration control system 22 such as is shown in detail in FIG. 2 for an eight cylindered engine may be employed. in FIG. 2, a shaft 100 driven by the engine crankshaft for example rotates at engine speed. It carries a contact 102, which successively closes the connection with switch contacts respectively 104, 106, 107, 108, and 110. Switch contacts 104, 106, 108, and 110 are disposed at quadrant positions around the shaft 100. Contact 107 is disposed at a location relative to contact 104 which represents the maximum number of crankshaft degrees over which injection is required to occur. Contact 108 is connected in parallel with contact 104 and contact 106 and contact 110 are connected in parallel.

Contact 104 is connected to a pulse generator 112. When contact 102 makes connection with contact 104, pulse generator 112 is energized to generate a pulse.

This pulse serves to reset a first ramp generator 114 and a second ramp generator 116, and is applied to a time delay circuit 118, to be delayed for a predetermined interval. The interval is the time required to reset the two ramp generators (for example, 5 to microseconds). Thereafter, the output of the time delay circuit starts both ramp generators generating a voltage having a ramp wave shape.

Ramp generators, such as pulse generators, are circuits which are well known in the electronic art and are capable of generating a voltage having the waveform of a single tooth of a sawtooth.

The output of the second ramp generator 116 is applied to a first voltage comparator 120. The output of the first ramp generator 114 is applied to a sample and hold circuit 122.

When the rotating contact 102 makes connection with a contact 106, a signal is generated which causes a pulse generator 124 to provide a pulse at its output. This pulse resets a third ramp generator 126 and is also applied to a time delay 128. After the time required for the third ramp generator 126 to be reset, the time delay output starts the third ramp generator generating a ramp waveform voltage output. This is applied to a voltage comparator 130.

The output of the time delay circuit 118, in addition to starting the first and second ramp generators is also applied to first and third transformer primary windings respectively 131 and 133. The output of the time delay circuit 128 is also applied to second and fourth trans former primary windings respectively 132 and 134. The respective primary windings 131, 132, 133, 134 are coupled to transformer secondary windings 141, 142, 143, 144. These secondary windings respectively energize valve signal generators 151, 152, 153, 154. An engine driven rotating selector switch 146, driven at onehalf engine speed will connect the proper one of primary windings 131, 132, 133, 134 to ground. Thus, when the output from pulse generator 112 is applied through time delay circuit 118 to the primary windings 131 and 133, current will flow through the one of these which is connected to ground at the time by the selector switch 146. A similar operation occurs with primary transformers 132 and 134. Thus only one of the primary windings 131 134 is energized at any given time, and accordingly only one of the valve signal generators is energized at any given time.

While the term valve signal pulse generator is employed for the structures 151, through 154, it should be understood that these represent power supplies or energy sources for operating the fuel injector valves which can be employed with this system. These are turned on by one input signal and are turned off thereafter by another signal. 1f the fuel injector valves are of the type that are solenoid operated, then these power sources supply the power for operating solenoids. 1f the fuel injector valves are of the piezoelectric type then power supplies furnish the energy for the piezoelectric types. If the fuel injection valves are hydraulically actuated then the indicated circuits are power sources for such hydraulically actuated valves.

The output of each valve signal generator 151 through 154 is applied to a distributor 160. The distributor distributes the four successive valve signals successively to eight electrically operated fuel injection valves.

When the contact 102 connects with the contact 107, a pulse generator 121 is energized. This applies an output which stops the first ramp generator 114 and energizes a sample and hold circuit 122 to sample the output of the first ramp generator at that time and to hold the level of that voltage. The output of the sample and hold circuit is a voltage whose amplitude at any one speed represents the maximum number of crank angle degrees over which a fuel injection valve will be held open and it varies inversely with speed. The sample and hold output is applied to a circuit designated as valve open duration compensation circuit 140. This circuit, the details of which will be shown later, provides the operation of multiplying the output of the sample and hold circuit 122 by the square root of the fraction Pv/Pa where Pv is the output of the first or third pressure sensor, (whichever is greater) and Pa is the voltage output of the second pressure sensor. The voltage from the first or third pressure sensors is indicative of the signaled fuel pressure while the voltage from the second pressure sensor is indicative of the actual fuel pressure.

The voltage, which is the output of the valve open duration circuit, 140, is applied to the respective voltage comparators 120 and 130. When the second ramp generator output voltage equals the voltage representing the computed valve open interval, then there is an output from the first voltage comparator which terminates the application of potential from the respective valve signal generator circuits 151 and 153. Similarly when the output of the third ramp generator equals the output of the valve open duration compensation circuit, then the valve signal generating circuits 152 and 154 have their outputs terminated.

The computed valve open interval is altered once per revolution of the engine crankshaft and thus is constantly updated.

To summarize the operation of the circuits shown in FIG. 2, the switch 102 successively makes contact with switches 104, 106, 107, 108 and 110. Contact with switches 104 and 106 thereafter causes the generation of signals which turn on power supplies which open injection valves and which fire ramp generators. Contact with a switch 107 establishes a signal whose amplitude varies with speed and whose amplitude at any one speed represents the maximum number of crankshaft degrees over which injection is required to occur. The valve open duration compensation circuit reduces the maximum fuel injection valve open time by the square root of the ratio of signalled fuel pressure to actual fuel pressure. The resulting voltage then represents the actual injection valve open time which should be used. When this interval has elapsed, as measured by the first and second voltage comparators, the comparator outputs are used to turn off the power supplies which opened the fuel injection valves.

Switch contacts 108 and 110 are in parallel with switch contacts 104 and 106 and thus provide four pulse intervals for each rotation of the crankshaft. The outputs of the valve signal generating circuits 151, 152, 153 and 154 are applied to a distributor 160.

A suitable fuel injection valve which may be electrically controlled by the output of the pulse generator circuits in accordance with this invention may be valves of the type described, for example, in allowed application Ser. No. 676,458 by N. Katchee filed Oct. 19, 1967, now US. Pat. No. 3,465,732 or application Ser. No. 671,065 by G. Benson filed Sept. 27, 1967, now US. Pat. No. 3,501,899, both applications being owned by a common assignee. Another type of fuel injection valve which may be suitable is described in US. Pat. No. 2,980,090 to Sutton et al.

The distributor 160 connects each of the valve signal generators to each of the fuel injector valves in a manner that feeds electrical energy as follows:

Valve signal generator 151 to a first fuel injector triggered by switch 104.

Valve signal generator 152 to a second fuel injector,

which is triggered by switch 106.

Valve signal generator 153 to a third fuel injector,

triggered by switch 108. Valve signal generator 154 to a fourth fuel injector, triggered by switch 110. Valve signal generator 151 to a fifth fuel injector,

triggered by switch 104.

Valve signal generator 152 to a sixth fuel injector,

triggered by switch 106. 7

Valve signal generator 153 to a seventh fuel injector,

triggered by switch 108.

Valve signal generator 154 to an eighth fuel injector,

triggered by switch 110.

The distributor can be any known type of switching system which is timed by the engine rotation.

Reference is now had to FIGS. 3 through 10 which show an arrangement. in accordance with this invention, for providing control of the duration of the opening ofa fuel injection valve over a predetermined crank angle, as modified by the square root of the ratio of the signalled fuel pressure to the actual fuel pressure. In other words. the structure shown in FIGS. 3 through 10 and the associated explanatory drawings which follow, takes the place of the structure shown in FIG. 2 and are illustrated by way of example for an eight cylindered engine.

FIG. 3 is a cross-sectional view of a fuel injection valve duration control system. FIG. 4 is a view along the lines 4-4 of FIG. 3. FIG. 5 is a partial section of FIG. 3. FIG. 6 is an end view of FIG. 3 and FIG. 7 is a view along the lines 7-7 of FIG. 6. A housing centrally supports therein on suitable bearings such as 172, a ported shaft 176. The shaft is rotatably driven by a drive pulley 178, which is driven at one-half crankshaft speed from the crankshaft. A sleeve is supported on the ported shaft within the housing 170, in a manner to be independently rotatable of the ported shaft.

A positive displacement pump 186 is driven from the rotating shaft 176 and pumps oil from a reservoir 188 into a passageway 190 (see FIG. 7), which is in the housing 170. This passageway in the housing'communicates with a passageway 192 in the ported shaft and also with a passageway 193 whose purpose will be explained later. The passageway 192 in the ported shaft, communicates via a passageway 194, successively, to each of eight passageways 198, which are radially formed in the housing, and which connect to each of eight radial ports 200 in said housing. Each of the eight radial ports are connected to the valve chambers of the eight fuel injection valves, previously mentioned, for providing the required fluid pressure for operating these eight valves sequentially. Upon the application of fluid to the chamber of the valve, the valve is lifted and the common fuel supply line, as shown in FIG. 1, is thereby connected to a delivery orifice causing fuel to be discharged into a cylinder.

The positive displacement pump 186 may be fitted with a pressure accumulator 187, in well known fashion, to provide energy capacity. As passageway 202, which communicates with the passageway 198 in the housing, provides communication with a smaller pressure accumulator mechanism 204, which insures maintenance of pressure in the valve chamber, when the axial supply channel 198 has been occluded by continued rotation of the ported shaft.

The axially extending channel 202 extends from the valve pressure accumulator 204 via a passageway 206, and radial passage 207 through a peripheral groove and opening in the sleeve 180, (as is more clearly seen 'in FIG. 4) to a radial channel 210, in the ported shaft, which connects to an axial channel 212, which in turn connects through another radial channel 214, to a channel 216 (shown in dotted lines) in the housing, which returns the oil back to the reservoir. It should be understood that even though the passageway 198 is occluded as the shaft 176 continues to rotate, the hydraulically operated valve which has been opened will more clear as this description progresses, there is provided a peripheral groove and an opening in the sleeve 180 for each cylinder.

The operation of the system is such that a release in the fluid pressure applied to a valve and a return path to the fluid reservoir is provided after a maximum interval of about 75 of shaft rotation following opening of the first radial ports.

FIG. 4 is a view along the line 4-4 of FIG. 3 illustrating a cross-section of the housing and sleeve. FIG. 8A is a view along the line 88 of FIG. 3. FIG. 8B is a re peat view along the line 9- 9 of FIG. 3. FIG. 9 is a view in elevation of the sleeve. FIG. 4 illustrates how the housing and sleeve cooperate to relieve the hydraulic pressure on the fuel valves whereby they are permitted to close. FIGS. 8A, 8B and 9 illustrate the groove and hole pattern whereby timing is achieved. It will be seen in FIG. 4 and FIGS. 8A, 8B and 9 that there are two sets of four spaced grooves respectively 220A, 2208, 220C, 220D, and 222A, 2228, 222C, and 222D, which are spaced around the periphery of the sleeve. Each one of these grooves extends for approximately 75 of angular length. At one end of each groove is a port or relief passage respectively 224A through 224D and 226A through 226D, for example, which passes radially through the sleeve. In the ported shaft there are respective relief passages 211 and 210 for each set of four grooves and four ports. Each port 224A through 224D communicates in sequence with the relief passageway 211 within the rotating shaft as the shaft rotates. Each port 226A through 226D communicates with relief passage 210 in sequence as the ported shaft is rotated. The reason that there are two sets of displaced radial grooves, is that there is not enough space around the periphery of the shaft for providing eight grooves, one for each valve, which will extend approximately 75 of the sleeve periphery which is required for an eight cylinder engine. Accordingly, four of these grooves and the four ports in the sleeve operate for providing relief to four fuel injection valves, and the remaining four grooves and ports in the sleeve provide relief for the remaining four fuel injection valves. The four ports of each set are symmetrically positioned in each trans verse plane and are offset by 45 from their counterparts in the other set. This configuration prevents overlapping of two ports (which must be spaced 45 apart on eight cylinder engine) by the sleeve grooves which are approximately 75 in angular length.

As may be seen in FIG. and FIG. 9, one end of the sleeve 180 has gear teeth 230, which are required in order that the sleeve may be rotated by a rack through angles up to 75, whereby the radial port in the sleeve at the end of a particular groove, may be brought into closer angular relationship with the passageway 207 or the angular relationship may be increased. In this manner, the crankshaft angle over which a fuel injection valve remains open is determined.

A position control system 232, hydraulically controls a rack gear 240, which extends through an opening 242 in the housing, to engage the gear teeth 230 on the end of the sleeve 180. The rack position control system is shown in FIG. 10. The rack position control system may use a hydraulic motor for which oil under pressure may be derived from pump 186 via passageways 190 and 193 (see FIG. 7). The rack position control opens a valve to a passageway 241 or 243 to enable hydraulic fluid to enter the piston chamber 245 and act on the piston 247 to position it at a desired location. The piston 247 is attached to the rack gear 240.

Referring now to FIG. 10, there is shown a circuit for l. e enta ixsqf V fli'a This circuit may also be used in the valve operation duration control circuit 140, shown in FIG. 2. The output of the first pressure sensor 60 is fed to an amplifier 250, the output from which is fed to a second amplifier 252, which in turn applies its output to a diode 254. The output of the third pressure sensor is applied to an amplifier 256, the output of which is amplifiedby amplifier 258, the output of which is applied to a second diode 260. The two diodes have their outputs connected together and then, through a resistor 262, to the input to an amplifier 264. The connection of the two diodes has the effect that whichever has the greater signal applied to it will block the lesser signal from the other diode. Thus, whenever the output of the third pressure sensor exceeds the output of the first pressure sensor, it is the third pressure sensor output which drives the amplifier 264. Whenever the third pressure sensor output is less than the first pressure sensor output, then it is the first pressure sensor output which drives the amplifier 264.

The second pressure sensor 72, applies its output to an amplifier 266, the output of which is amplified by amplifier 268. The output of the amplifier 268 is applied as one input to a multiplier circuit 270 which is in the negative feedback path of the amplifier. The second input ti) the multiplier circuit 270 is the output of the amplifier 264. Multiplier circuit 270 output is summed with the output of either diode 254 or 260 and is applied as the input to the amplifier 264. The arrangement shown serves the function of dividing the output of the first or third pressure sensor by the output of the second pressure sensor, as the case may be.

The output of amplifier 264 is summed with the output of another multiplier circuit 272 which is in the negative feedback path of an amplifier 280. The resultant is applied to the input of the amplifier 280. The output of the amplifier 280 is applied to the two inputs of multiplier circuit 272.

The output of amplifier 280 is a signal representing VPWPE. It is applied to a level setting potentiometer 282. The theory and specific circuitry of the ratio and square root circuit arrangement described is found described at length in an article Theory and Application of a Linear Four-Quadrant Monolithic Multiplier," by Edward L. Renschler, Pp 60, 67 published in EEE," Vol. 17, No. 5 in May, I969 (Mactier Publishing Corporation).

The foregoing arrangment is illustrative of one arrangement for accomplishing the signal processing and is not to be considered as the only way. In an all electrical system, such as shown in FIG. 2, the output from potentiometer 282 is the signal multiplied by the sample and hold circuit 122 output, to provide a resultant signal. This is shown as the output of the circuit in FIG. 2, which is applied to the comparator I20 and 130.

For the fluid valve control system, the output of the potentiometer 282 is applied to an amplifier 28 3-. One output terminal of the amplifier is connected to a winding of a differential coil hydraulic valve 286 and also to a capacitor 288. The other output of the amplifier is connected to a resistor 290, the other end of which is connected to ground.

A linear potentiometer 292 has its sliding arm 294 connected to be positioned in accordance with the position of piston 217 (FIG. 5). A source of potential 296 is connected across the potentiometer 292. The sliding arm 294 is electrically connected to an amplifier 298. One output terminal of amplifier 298 is connected to another winding of the magnetically controlled hydraulic valve 286. The other amplifier output terminal is connected to the resistor 290.

The magnetically controlled hydraulic valve is a well known device which controls the application of hydraulic fluid to the piston chamber 245 (FIG. 5) to position the piston 247 (FIG. 5) in response to the difference of the two electrical inputs. Here one input instructs the valve where the piston is to be positioned and the other input is a feedback signal indicative as to the actual piston position. The arrangement shown is a well known servo arrangement for establishing the position of a device in response to an electrical signal.

FIG. 11 is a cross-sectional view of a fuel injection valve which may be used with the embodiments of this invention. A piston motor or source of hydraulic pressure is used to actuate a piston 302. The piston motor may be piezoelectric, electromagnetic or electrostrictive if electrical operation is desired. The source of hydraulic pressure may be a system such as shown in FIGS. 3 through herein.

Housing walls 304 define a piston chamber 306 having an opening 308 at the base thereof which communicates with a chamber 310 in the center of the valve body. The valve body has walls 312 with a central cavity, a tapped opening in the walls at the top in which a mechanical stop screw 314 is threaded, an opening in the walls at one side to afford communication of the central cavity with the opening 308. An opening is provided on the other side to afford communication with a temperature compensating arrangement 316 consisting of a piston 3K8 whose position is varied in response to a spring 230.

The lower portion of the housing walls provide a fuel inlet opening 322 and a fuel outlet opening 324. A rod member 326 is urged downwardly, to block the outlet opening, by a spring 327. The spring presses down on v a disc member 328 which rests on a first diaphragm 330. The central cavity space 310 between the first diaphragm 330 and a second diaphragm 332, is bridged by disc members 334 and 336. Discs 328, 334 and 336 are attached to each other and also to rod member 326 so that when the piston motor 300 actuates the piston 302, hydraulic fluid pressure caused in response thereto in the cavity between the diaphragms counteracts the pressure of spring 327 enabling rod member 326 to be lifted to permit fuel to pass from the inlet cavity through the orifice 333 and then through the outlet opening. When pressure on the piston 302 is relieved, the rod member 326 is moved by the spring 327 to close the outlet opening 324 against the pressure of the fuel on rod member 326. A vent 338 prevents bluid up of pressure beneath diaphragm 332 that would restrict closure of the outlet orifice.

There has accordingly been shown and described herein a novel and improved system for determining the amount of fuel to be introduced into a piston by a fuel injection valve.

What is claimed is: l. A system for controlling the amount of fuel introduced into the piston chamber of an internal combustion engine by a fuel injection valve comprising:

a source of fuel, means for continuously applying fuel under pressure to said fuel injection valve from said source,

means for generating a control effect proportional to direct measurement of the mass air flow to said engine,

means for varying the pressure of the fuel applied to said fuel injection valve by said means for applying fuel under pressure in proportion to said control effect, and

means for opening said fuel injection valve independently of fuel pressure applied thereto over an interval which varies inversely with engine speed.

2. A system as recited in claim 1 wherein said means for varying the pressure of the application of fuel by said means for applying fuel under pressure does not reduce the pressure of said fuel below a predetermined minimum value.

3. A system as recited inclaim 1 wherein there is included transducer means for establishing a first signal responsive to the square of mass air flow to said internal combustion engine which signal represents a desired fuel pressure,

transducer means for establishing a second signal responsive to fuel pressure applied to said fuel injection valve which signal represents actual fuel pressure,

means to which said first and second signals are ap plied for establishing a third signal respresentative of the square root of the ratio of said first and second signals, and

means for reducing each interval over which said fuel injection valve is maintained open to an amount proportional to the amplitude of said third signal.

4., A system as recited in claim I wherein said means for applying fuel under pressure to said fuel injection valve from said source includes a first passageway between said source of fuel and said fuel injection valve,

pump means for applying fuel under pressure from said source to said first passageway, and

a second passageway communicating with and extending from said first passageway toward said source of fuel;

said means for varying the pressure of the application of fuel includes a controllable spill valve coupling to said second passageway with said source of fuel.

5. A system as recited in claim 1 wherein said means for opening said fuel injection valve for a time varies inversely with the speed of said engine includes:

means for generating a time signal having an amplitude proportional to the time required for said engine to rotate through a predetermined crank angle,

transducer means for establishing a first signal responsive to the square of mass air flow to said internal combustion engine which signal represents a desired fuel pressure,

transducer means for establishing a second signal responsive to fuel pressure applied to said fuel injection valve which signal represents actual fuel pressure,

means to which said first and second signals are applied for establishing a third signal having an amplitude representative of the square root of the ratio of said first and second signals,

means for reducing the amplitude of said time signal by said third signal amplitude,

a ramp voltage generator,

means responsive to said engine attaining a predetermined point in a cycle of its operation for generating a valve opening signal and for initiating operation of said ramp voltage generator,

comparator means for comparing the output of said ramp voltage generator with said reduced time signal and producing a valve closing signal when they are equal, and

means for applying said valve opening signal and thereafter said valve closing signal to said fuel injector valve causing it to open and then close in response thereto.

6. A system as recited in claim 1 wherein said means for opening said fuel injection valve for a time which varies inversely with the speed of said engine includes a source of a hydraulic fluid under pressure,

means for applying hydraulic fluid under pressure from said source to said fuel injection valve to maintain said fuel injection valve upon the crankshaft of said engine attaining a first predetermined position in its cycle of operation,

means for relieving the pressure of said hydraulic fluid applied to said fuel injection valve when said engine attains a second predetermined position in its cycle of operation.

7. A system as recited in claim 6 wherein said means for applying hydraulic fluid under pressure from said source to said fuel injection valve to maintain said valve open upon the crankshaft of said engine attaining a first predetermined position in its cycle of operation includes:

a housing having walls surrounding a central cavity therein,

a ported shaft rotatably supported within said central cavity,

means for rotatably driving said ported shaft from said engine,

a first passageway extending through said housing walls to said ported shaft,

means coupling said valve to said first passageway on the outside opening of said housing,

an axial passageway in said ported shaft extending from said source of fluid under pressure part way through said ported shaft, and

a radial passageway extending from said axial passageway in said ported shaft to communicate with said first passageway for every cycle of rotation of said ported shaft to enable application of fluid under pressure to said hydraulic fuel injection valve.

8. A system as recited in claim 7 wherein said means for relieving the pressure of said hydraulic fluid applied to said fuel injection valve when said engine attains a ing for a predetermined distance along a circumference of said sleeve;

a fourth pressure relief passageway extending frorh one end of said groove radially through said sleeve to communicate with the other end of said second pressure relief passageway in said ported shaft at least once during rotation of said ported shaft;

a fifth pressure relief passageway coupling said first passageway extending through said housing walls to said groove in said sleeve periphery;

motor means for moving said sleeve over an arc defined by said radial groove to position said fourth passageway in said sleeve at a desired location along the rotational path of said second relief passageway in said ported shaft; and

means for controlling said motor means.

9. A system as recited in claim 8 wherein said means for controlling said motor means includes:

transducer means for establishing a first signal responsive to the square of the mass air flow to said internal combustion engine which signal represents a desired fuel pressure;

transducer means for establishing a second signal responsive to fuel pressure applied to said fuel injection valve which signal represents actual fuel pressure;

means to which said first and second signals are applied for establishing a third signal representative of the square root of the ratio of said first and second signals; and

means for operating said motor responsive to said third signal to position the opening of said fifth pressure relief passageway at said groove a distance from the other end thereof which is proportional to the amplitude of said third signal.

10. In a system for introducing fuel into the piston chamber of 'an internal combustion engine of the type which rotates a crank shaft, wherein there is a fuel injection valve for ach piston chamber, and the fuel injection valves are supplied with fuel under pressure from a common passageway, the improvement comprising means for opening each fuel injection valve over an interval required for said engine to operate through a predetermined crank shaft angle including,

means for establishing for each cycle of rotation of said crank shaft a first timing signal having an amplitude representative of the maximum desirable open interval of said fuel injection valves for the speed at which said engine is then operating;

means for successively opening each fuel injection valve at a predetermined point in the cycle of operation of said crank shaft;

means for generating for each opened fuel injection valve a second timing signal whose amplitude starts from an initial value less than said first timing signal and increases in amplitude with the passage of time;-

means for comparing the amplitude of said first timing signal with the amplitude of each of said second timing signals and producing a fuel injection valve closing signal when they are equal, and

means for modifying said interval by an amount determined by the square root of the ratio of the square of the mass air flow to said internal combustion engine and the pressure of the fuel being supplied to the common passageway.

11. In a system as recited in claim 10 wherein said means for modifying said interval by an amount deter mined by the square root of the ratio of the square of the mass air flow to said internal combustion engine and the pressure of the fuel being supplied to the common passageway includes:

means establishing a venturi passageway in the air intake passageway to said engine;

first transducer means responsive to the air flow through said venturi passageway for generating a first electrical signal responsive to the air flow therethrough;

second transducer means responsive to the pressure of the fuel in said common passageway for generating a second electrical signal;

means to which said first and second electrical signals are applied for generating a third signal representative of the ratio thereof;

means responsive to said third signal for generating a fourth signal representative of the square root thereof; and

means for reducing said first timing signal amplitude by the amplitude of said fourth signal.

12. In a system as recited in claim 11 wherein there is included a fourth transducer means responsive to the air flow through the air intake passageway downstream of said venturi passageway for establishing a fifth electrical signal representative thereof; and

means for determining which is the larger of said fifth signal and said second signal; and

means for applying the fifth signal to said means to which said first and second signals are applied in place of said second signal when it is the larger.

13. In a system for controlling the amount of fuel introduced into the piston chambers of an internal combustion engine by fuel injection valves which are supplied fuel under pressure from a common rail having one end connected to a fuel pump and the other end to a spill valve, fuel passing through the spill valve being collected in a reservoir said pump pumping fuel from said reservoir;

said spill valve being controlled by the differential air pressure applied to a diaphragm between a venturi passageway formed in the air intake passageway for said engine and a location in said air intake passageway preceding said venturi passageway;

the improvement comprising means for opening each fuel injection valve over an interval required for said engine to rotate its crank shaft through a predetermined crank shaft angle; and

means for modifying said interval over which each fuel injection valve is open by an amount determined by the square root ofthe ratio of the square of the mass air flow through said venturi passageway and the pressure of fuel being applied to said fuel injection valves including a first transducer coupled to said venturi passageway for generating a first signal representative of the mass air flow therethrough;

a second transducer coupled to said spill valve for generating a second signal representing actual fuel pressure;

a third transducer coupled to said air intake passageway downstream of said venturi passageway for measuring idling air flow pressure and producing a third signal representative thereof;

comparator means to which said second and third signals are applied for producing an output which is the larger of the two;

ratio means to which said comparator means output and said first signal is applied for producing an out put which is the ratio of its inputs;

square root means to which said ratio means output is applied for producing an output which is the square root of its input; and

means responsive to the output of said square root means for modifying the interval over which each fuel injection valve is opened.

14. In a system as recited in claim 13 wherein there is included a choke valve in the engine air intake passageway positioned between said venturi passageway and the location in said air intake passageway which is used to establish differential pressure for said spill valve whereby upon starting said engine when said choke is closed said spill valve will be principally controlled by the air pressure at said location.

15. A system for controlling the amount of fuel introduced into the piston chambers of an internal combustion engine by a fuel injection valve for each piston chamber, said fuel injection valves being supplied fuel under pressure from a common rail having one end connected to a fuel pump and the other end to a spill valve, fuel passing through said spill valve into a reservoir from which said fuel pump pumps fuel under pressure into said common rail the improvement comprising:

means responsive to the mass air flow to said engine for generating a control effect proportional to the direct measurement thereof,

means for controlling said spill valve responsive to said control effect to control the amount of fuel passed by said spill valve and thereby the pressure of fuel applied to said fuel injection valves, and

means for opening each of said fuel injection valves over an interval which varies inversely with engine speed.

16. A system as recited in claim 15 wherein said means for controlling said spill valve includes means for controlling said spill valve for enabling a predetermined minimum fuel pressure to be applied to said fuel injection valves.

17. A system as recited in claim 16 wherein said means proportional to the mass air flow to said engine includes a first transducer for generating a first signal representative thereof, and

said system includes a second transducer for sensing the pressure of fuel in said common rail and producing a second signal representative thereof,

computer means to which said first and second signals are applied for determining an interval over which said fuel injection valves should remain open, and producing an output representative thereof,

means responsive to said computer means output for accordingly modifying the interval over which each said fuel injection valve remains open, 18. A system for controlling the amount of fuel introduced into the piston chamber of an internal combustion engine by a fuel injection valve, said system comprising:

a source of fuel, means for continuously applying fuel under pressure to said fuel injection valve from said source,

means responsive to the mass air flow to said engine for generating a control signal proportional thereto,

means responsive to said control signal to vary the pressure of fuel applied to said fuel injection valve above a predetermined pressure,

means for generating a pressure signal representative of the pressure of the fuel applied to said fuel injection valve, means for generating a first time signal having a duration that varies inversely with engine speed,

computer means responsive to said control signal and to said pressure signal for producing a second time signal representative of an interval over which said fuel injection valves should remain open when said fuel pressure is at or below said predetermined pressure, and

means responsive to said first and second time signals for opening said fuel injection valve over an interval determined by the duration of said first time sig nal when said fuel pressure exceeds said predeter mined pressure and which is equal to the interval represented by said second time signal when said fuel pressure is at or below said predetermined pressure.

19. A system for controlling the amount of fuel introduced into the piston chambers of an internal combustion engine by a fuel injection valve for each piston chamber, said fuel injection valves being supplied fuel under pressure from a common rail having one end connected to a fuel pump and the other end to a spill valve, fuel passing through said spill valve into a reservoir from which said fuel pump pumps fuel under pressure into said common rail, the improvement compris ing:

means responsive to the mass air flow to said engine for generating a control signal proportional thereto, means responsive to said control signal to control the amount of fuel passed by said spill valve up to a predetermined maximum value and thereby to control the pressure of said fuel down to a predetermined minimum value applied to said fuel injection valves, means for generating a signal representative of the pressure of the fuel applied to said fuel injection valves, means for generating a crank angle signal whose amplitude increases over an interval required for said engine to rotate through a fixed crank angle, computer means responsive to said control signal and to said signal representative of fuel pressure for producing a time signal representative of an interval over which said fuel injection valve should remain open when said fuel pressure is at or below said predetermined pressure, means for selectively operating said fuel injection valve each time said means for generating a crank angle signal commences to operate, means for comparing said crank angle signal with said time signal and producing a comparator signal when they have equal amplitudes, and means for closing said fuel injection valves responsive to said comparator signal]. l= =l 

1. A system for controlling the amount of fuel introduced into the piston chamber of an internal combustion engine by a fuel injection valve comprising: a source of fuel, means for continuously applying fuel under pressure to said fuel injectiOn valve from said source, means for generating a control effect proportional to direct measurement of the mass air flow to said engine, means for varying the pressure of the fuel applied to said fuel injection valve by said means for applying fuel under pressure in proportion to said control effect, and means for opening said fuel injection valve independently of fuel pressure applied thereto over an interval which varies inversely with engine speed.
 2. A system as recited in claim 1 wherein said means for varying the pressure of the application of fuel by said means for applying fuel under pressure does not reduce the pressure of said fuel below a predetermined minimum value.
 3. A system as recited in claim 1 wherein there is included transducer means for establishing a first signal responsive to the square of mass air flow to said internal combustion engine which signal represents a desired fuel pressure, transducer means for establishing a second signal responsive to fuel pressure applied to said fuel injection valve which signal represents actual fuel pressure, means to which said first and second signals are applied for establishing a third signal respresentative of the square root of the ratio of said first and second signals, and means for reducing each interval over which said fuel injection valve is maintained open to an amount proportional to the amplitude of said third signal.
 4. A system as recited in claim 1 wherein said means for applying fuel under pressure to said fuel injection valve from said source includes a first passageway between said source of fuel and said fuel injection valve, pump means for applying fuel under pressure from said source to said first passageway, and a second passageway communicating with and extending from said first passageway toward said source of fuel; said means for varying the pressure of the application of fuel includes a controllable spill valve coupling to said second passageway with said source of fuel.
 5. A system as recited in claim 1 wherein said means for opening said fuel injection valve for a time varies inversely with the speed of said engine includes: means for generating a time signal having an amplitude proportional to the time required for said engine to rotate through a predetermined crank angle, transducer means for establishing a first signal responsive to the square of mass air flow to said internal combustion engine which signal represents a desired fuel pressure, transducer means for establishing a second signal responsive to fuel pressure applied to said fuel injection valve which signal represents actual fuel pressure, means to which said first and second signals are applied for establishing a third signal having an amplitude representative of the square root of the ratio of said first and second signals, means for reducing the amplitude of said time signal by said third signal amplitude, a ramp voltage generator, means responsive to said engine attaining a predetermined point in a cycle of its operation for generating a valve opening signal and for initiating operation of said ramp voltage generator, comparator means for comparing the output of said ramp voltage generator with said reduced time signal and producing a valve closing signal when they are equal, and means for applying said valve opening signal and thereafter said valve closing signal to said fuel injector valve causing it to open and then close in response thereto.
 6. A system as recited in claim 1 wherein said means for opening said fuel injection valve for a time which varies inversely with the speed of said engine includes a source of a hydraulic fluid under pressure, means for applying hydraulic fluid under pressure from said source to said fuel injection valve to maintain said fuel injection valve upon the crankshaft of said engine attaining a first predetermined position in its cycle of operation, means for relieving the Pressure of said hydraulic fluid applied to said fuel injection valve when said engine attains a second predetermined position in its cycle of operation.
 7. A system as recited in claim 6 wherein said means for applying hydraulic fluid under pressure from said source to said fuel injection valve to maintain said valve open upon the crankshaft of said engine attaining a first predetermined position in its cycle of operation includes: a housing having walls surrounding a central cavity therein, a ported shaft rotatably supported within said central cavity, means for rotatably driving said ported shaft from said engine, a first passageway extending through said housing walls to said ported shaft, means coupling said valve to said first passageway on the outside opening of said housing, an axial passageway in said ported shaft extending from said source of fluid under pressure part way through said ported shaft, and a radial passageway extending from said axial passageway in said ported shaft to communicate with said first passageway for every cycle of rotation of said ported shaft to enable application of fluid under pressure to said hydraulic fuel injection valve.
 8. A system as recited in claim 7 wherein said means for relieving the pressure of said hydraulic fluid applied to said fuel injection valve when said engine attains a second predetermined position in its cycle of operation comprises: a sleeve rotatably supported on said ported shaft within said central cavity; a first pressure relief passageway extending through said housing walls to said source; a second pressure relief passageway in said ported shaft having one end extending to communicate with said first pressure relief passageway; a groove in the outer periphery of said sleeve extending for a predetermined distance along a circumference of said sleeve; a fourth pressure relief passageway extending from one end of said groove radially through said sleeve to communicate with the other end of said second pressure relief passageway in said ported shaft at least once during rotation of said ported shaft; a fifth pressure relief passageway coupling said first passageway extending through said housing walls to said groove in said sleeve periphery; motor means for moving said sleeve over an arc defined by said radial groove to position said fourth passageway in said sleeve at a desired location along the rotational path of said second relief passageway in said ported shaft; and means for controlling said motor means.
 9. A system as recited in claim 8 wherein said means for controlling said motor means includes: transducer means for establishing a first signal responsive to the square of the mass air flow to said internal combustion engine which signal represents a desired fuel pressure; transducer means for establishing a second signal responsive to fuel pressure applied to said fuel injection valve which signal represents actual fuel pressure; means to which said first and second signals are applied for establishing a third signal representative of the square root of the ratio of said first and second signals; and means for operating said motor responsive to said third signal to position the opening of said fifth pressure relief passageway at said groove a distance from the other end thereof which is proportional to the amplitude of said third signal.
 10. In a system for introducing fuel into the piston chamber of an internal combustion engine of the type which rotates a crank shaft, wherein there is a fuel injection valve for ach piston chamber, and the fuel injection valves are supplied with fuel under pressure from a common passageway, the improvement comprising means for opening each fuel injection valve over an interval required for said engine to operate through a predetermined crank shaft angle including, means for establishing for each cycle of rotation of said crank shaft a first timing signal hAving an amplitude representative of the maximum desirable open interval of said fuel injection valves for the speed at which said engine is then operating; means for successively opening each fuel injection valve at a predetermined point in the cycle of operation of said crank shaft; means for generating for each opened fuel injection valve a second timing signal whose amplitude starts from an initial value less than said first timing signal and increases in amplitude with the passage of time; means for comparing the amplitude of said first timing signal with the amplitude of each of said second timing signals and producing a fuel injection valve closing signal when they are equal, and means for modifying said interval by an amount determined by the square root of the ratio of the square of the mass air flow to said internal combustion engine and the pressure of the fuel being supplied to the common passageway.
 11. In a system as recited in claim 10 wherein said means for modifying said interval by an amount determined by the square root of the ratio of the square of the mass air flow to said internal combustion engine and the pressure of the fuel being supplied to the common passageway includes: means establishing a venturi passageway in the air intake passageway to said engine; first transducer means responsive to the air flow through said venturi passageway for generating a first electrical signal responsive to the air flow therethrough; second transducer means responsive to the pressure of the fuel in said common passageway for generating a second electrical signal; means to which said first and second electrical signals are applied for generating a third signal representative of the ratio thereof; means responsive to said third signal for generating a fourth signal representative of the square root thereof; and means for reducing said first timing signal amplitude by the amplitude of said fourth signal.
 12. In a system as recited in claim 11 wherein there is included a fourth transducer means responsive to the air flow through the air intake passageway downstream of said venturi passageway for establishing a fifth electrical signal representative thereof; and means for determining which is the larger of said fifth signal and said second signal; and means for applying the fifth signal to said means to which said first and second signals are applied in place of said second signal when it is the larger.
 13. In a system for controlling the amount of fuel introduced into the piston chambers of an internal combustion engine by fuel injection valves which are supplied fuel under pressure from a common rail having one end connected to a fuel pump and the other end to a spill valve, fuel passing through the spill valve being collected in a reservoir said pump pumping fuel from said reservoir; said spill valve being controlled by the differential air pressure applied to a diaphragm between a venturi passageway formed in the air intake passageway for said engine and a location in said air intake passageway preceding said venturi passageway; the improvement comprising means for opening each fuel injection valve over an interval required for said engine to rotate its crank shaft through a predetermined crank shaft angle; and means for modifying said interval over which each fuel injection valve is open by an amount determined by the square root of the ratio of the square of the mass air flow through said venturi passageway and the pressure of fuel being applied to said fuel injection valves including a first transducer coupled to said venturi passageway for generating a first signal representative of the mass air flow therethrough; a second transducer coupled to said spill valve for generating a second signal representing actual fuel pressure; a third transducer coupled to said air intake passageway downstream of said venturi passageway for measuring idling air flow pressure and producing a Third signal representative thereof; comparator means to which said second and third signals are applied for producing an output which is the larger of the two; ratio means to which said comparator means output and said first signal is applied for producing an output which is the ratio of its inputs; square root means to which said ratio means output is applied for producing an output which is the square root of its input; and means responsive to the output of said square root means for modifying the interval over which each fuel injection valve is opened.
 14. In a system as recited in claim 13 wherein there is included a choke valve in the engine air intake passageway positioned between said venturi passageway and the location in said air intake passageway which is used to establish differential pressure for said spill valve whereby upon starting said engine when said choke is closed said spill valve will be principally controlled by the air pressure at said location.
 15. A system for controlling the amount of fuel introduced into the piston chambers of an internal combustion engine by a fuel injection valve for each piston chamber, said fuel injection valves being supplied fuel under pressure from a common rail having one end connected to a fuel pump and the other end to a spill valve, fuel passing through said spill valve into a reservoir from which said fuel pump pumps fuel under pressure into said common rail the improvement comprising: means responsive to the mass air flow to said engine for generating a control effect proportional to the direct measurement thereof, means for controlling said spill valve responsive to said control effect to control the amount of fuel passed by said spill valve and thereby the pressure of fuel applied to said fuel injection valves, and means for opening each of said fuel injection valves over an interval which varies inversely with engine speed.
 16. A system as recited in claim 15 wherein said means for controlling said spill valve includes means for controlling said spill valve for enabling a predetermined minimum fuel pressure to be applied to said fuel injection valves.
 17. A system as recited in claim 16 wherein said means proportional to the mass air flow to said engine includes a first transducer for generating a first signal representative thereof, and said system includes a second transducer for sensing the pressure of fuel in said common rail and producing a second signal representative thereof, computer means to which said first and second signals are applied for determining an interval over which said fuel injection valves should remain open, and producing an output representative thereof, means responsive to said computer means output for accordingly modifying the interval over which each said fuel injection valve remains open.
 18. A system for controlling the amount of fuel introduced into the piston chamber of an internal combustion engine by a fuel injection valve, said system comprising: a source of fuel, means for continuously applying fuel under pressure to said fuel injection valve from said source, means responsive to the mass air flow to said engine for generating a control signal proportional thereto, means responsive to said control signal to vary the pressure of fuel applied to said fuel injection valve above a predetermined pressure, means for generating a pressure signal representative of the pressure of the fuel applied to said fuel injection valve, means for generating a first time signal having a duration that varies inversely with engine speed, computer means responsive to said control signal and to said pressure signal for producing a second time signal representative of an interval over which said fuel injection valves should remain open when said fuel pressure is at or below said predetermined pressure, and means responsive to said first and second time signals for opening said fuel injection vAlve over an interval determined by the duration of said first time signal when said fuel pressure exceeds said predetermined pressure and which is equal to the interval represented by said second time signal when said fuel pressure is at or below said predetermined pressure.
 19. A system for controlling the amount of fuel introduced into the piston chambers of an internal combustion engine by a fuel injection valve for each piston chamber, said fuel injection valves being supplied fuel under pressure from a common rail having one end connected to a fuel pump and the other end to a spill valve, fuel passing through said spill valve into a reservoir from which said fuel pump pumps fuel under pressure into said common rail, the improvement comprising: means responsive to the mass air flow to said engine for generating a control signal proportional thereto, means responsive to said control signal to control the amount of fuel passed by said spill valve up to a predetermined maximum value and thereby to control the pressure of said fuel down to a predetermined minimum value applied to said fuel injection valves, means for generating a signal representative of the pressure of the fuel applied to said fuel injection valves, means for generating a crank angle signal whose amplitude increases over an interval required for said engine to rotate through a fixed crank angle, computer means responsive to said control signal and to said signal representative of fuel pressure for producing a time signal representative of an interval over which said fuel injection valve should remain open when said fuel pressure is at or below said predetermined pressure, means for selectively operating said fuel injection valve each time said means for generating a crank angle signal commences to operate, means for comparing said crank angle signal with said time signal and producing a comparator signal when they have equal amplitudes, and means for closing said fuel injection valves responsive to said comparator signal. 